1. Field of the Invention
The present invention relates to a liquid metal target forming apparatus that forms a liquid metal target by a flow of liquid metal such as liquid lithium.
2. Description of the Related Art
FIG. 13 is a configuration diagram illustrating an example of a related liquid metal loop. FIG. 14 is an explanatory diagram illustrating a discharge port of a nozzle of the liquid metal loop illustrated in FIG. 13. A liquid metal loop 500 includes a target 501 used to obtain a neutron by irradiating with a proton beam, a quench tank 502 disposed at a downstream side of the target 501, a circulating pump 503 including an electromagnetic pump connected to the quench tank 502, and a heat exchanger 504 disposed at a downstream side of the circulating pump 503. The target 501 pushes liquid lithium toward a curving back wall 505 made of SUS 304 using centrifugal force, and forms a liquid lithium film flow on the back wall 505. The target 501 includes a nozzle that ejects liquid lithium. As illustrated in FIG. 14, a discharge port 506 of the nozzle has a reed shape including a long side 507 and a short side 508. An upper portion of the long side 507 forms a free liquid level of the target, and the long side 507 is machine processed in a predetermined surface roughness to form a smooth free liquid level.
A diameter of the back wall 505 is about 250 mm, a maximum flow velocity of liquid lithium is 20 m/s, and the liquid lithium is inhibited from boiling by a pressure due to centrifugal force. Liquid lithium has a film thickness of about 25 mm, and a width of about 260 mm. When an accelerator causes a proton to collide with liquid lithium flowing on the back wall 505, a neutron is generated behind liquid lithium. The neutron penetrates the back wall 505, and the rear of the back wall is irradiated with the neutron.
When causing liquid lithium to flow on the back wall 505, it is devised so that a wave of the free liquid level is suppressed to a predetermined value or less. In a document D1 (IFMIF experimental study related to liquid metal lithium target flow, Horiike, Kondou, Kanamura et al., J. Plasma Fusion Res. Vol. 84, No. 9 (2008) 600-605), water is sprayed at different velocities on a back wall substantially horizontally disposed as an experimental device, and a state of the free surface wave is observed. A shape of a discharge port of a nozzle is a rectangle having a width of 70 mm, and a height of 10 mm. The free surface wave is photographed using a stroboscope by a CCD camera. As a result, it confirms that a wave is not generated at a flow velocity of 3.0 m/s, a small wave is generated at a flow velocity of 5.0 m/s or more, and an irregular wave appears on the entire free surface at a flow velocity of 9.0 m/s or more. Referring to a measurement result at the center of a flow passage, the height of the wave is within 1 mm even at a high flow velocity.
When an irradiation area which is irradiated with a proton beam on a target may be increased, neutron generation efficiency is improved. However, as disclosed in a document D2 (Japanese Laid-open Patent Publication No. 2002-64000), in a method of forming a film flow of liquid lithium by causing liquid lithium to flow at a high speed on the curving back wall 505, centrifugal force acts such that a free liquid level of liquid lithium sprayed from a rectangular nozzle becomes smooth. In addition, in an experiment of D1 which presumes that liquid lithium flows on a back wall, it confirms that a wave generated on a free surface of a lithium flow at a high speed is suppressed to 1 mm or less. In both cases, it is difficult to increase an irradiation area of a proton beam in a target. The invention is conceived to solve the problems.